1. Field of the Invention
The invention relates to a method for dissolving salt encrustations which are deposited on the heat-exchanging surfaces of a heat exchanger from a gas saturated with water vapor by exceeding the saturation limit.
2. Description of the Prior Art
Methods are known in which gases saturated with water vapor are heated by a heat exchange to a temperature which is suitable for the physical or chemical treatments of the gas. Recuperative heat exchangers such as block, plate or particularly tube-bundle heat exchangers are frequently used for this purpose. If the water vapor/gas mixture contains mineral salts, the solubility of which drops with increasing temperature or if the amount of solvent is decreased in the heat exchanger, the deposition of the mineral substance on the hot surface of the heat exchanger cannot, as a rule, be avoided because the solution is heated or the solvent evaporates. The crusts which are more or less hard substantially reduce the performance of the heat exchanger and it is therefore customary to clean the heat-exchanging surfaces periodically, for instance, by boiling with acid or alkaline solutions. Plants, for instance, chemical plants which contain such heat exchangers can accordingly be operated continuously only if a substitute heat exchanger is connected for the period of cleaning.
It is also known, especially for removal of water-soluble salt encrustations, to spray water or possibly also aqueous solutions on the heat exchanger surfaces without interrupting the operation, the crusts being removed by the force of the impinging fluid and its dissolving power. Disadvantages of this method are the cooling-off of the gas if the temperature of the spraying water is lower than the normal exit temperature of the gas and, above all, the lowering of the dew point or the oversaturation of the gas with the dissolving medium. Corrosion of apparatus, piping and the like which follow the heat exchanger, can then usually be prevented only by making these parts of the plant of corrosion-proof materials, which is a technically costly solution.